ScienceCBSE Class 8 · The Invisible Living World: Beyond Our Naked Eye

Cell Structure and Levels of Organisation: Class 8 Science

Updated 17 October 2026 · Fact-checked

The cell is the basic unit of life. A typical cell has a cell membrane, cytoplasm and a nucleus; plant cells also have a cell wall, plastids and a large vacuole. Cells of similar kind form a tissue, tissues form an organ, organs form an organ system, and organ systems together form the organism.

Both cells have a membrane, cytoplasm and nucleus; only the plant cell also has a cell wall, chloroplasts and a large vacuole.

Illustration drawn for QuestionBuddy.

Understand Cell Structure and Levels of Organisation

Seeing cells. The human eye cannot see very small things, so people learnt to use curved glass lenses (thick in the middle, thin at the edge, like a lentil seed) and then microscopes. In 1665 Robert Hooke published Micrographia. His microscope made things look 200 to 300 times bigger, and a thin slice of cork looked like a honeycomb of small empty spaces, which he called cells. Around the same time Antonie van Leeuwenhoek made better lenses and was the first to clearly describe bacteria and blood cells, so he is called the Father of Microbiology.

Parts of a cell (Activities 2.2 and 2.3). Onion peel cells are nearly rectangular and packed closely without gaps; cheek cells are thin, flat and polygon-shaped. Both show three basic parts.

Cell membrane: the outer layer; it is porous, enclosing the contents, separating one cell from another and allowing essential materials in and waste out.
Cytoplasm: the space between membrane and nucleus; it holds carbohydrates, proteins, fats and mineral salts, and most life processes take place here.
Nucleus: has its own thin membrane; it regulates all activities of the cell and also its growth.

Plant cells have more. A cell wall lies outside the membrane and gives rigidity and strength, which is why plant cells are compactly arranged and look firm. Plastids are rod-shaped structures; those with chlorophyll are chloroplasts (green, photosynthesis), while non-green plastids store substances. A large vacuole stores substances, removes waste and maintains the shape of the cell. Animal cells usually have no vacuole, or only small ones. Mitochondria are marked in the figure of both cells.

Shape matches function. A muscle cell is spindle-shaped, thin and flexible, which suits the wave-like contraction that pushes food down the food pipe. A nerve cell (neuron) is very long and branched so that it can reach different parts of the body and pass messages quickly. Cheek cells are thin and flat and form a protective lining. Some plant cells form long tubes that carry water.

Levels of organisation. Cell (basic unit, like a brick in a wall) → tissue (group of similar cells) → organ (different tissues together) → organ system (organs working for a major function) → organism. A multicellular organism begins from a single cell, the egg, which divides repeatedly. The yolk of an ostrich egg is a single cell of about 130 mm to 170 mm diameter, the largest known cell.

Bacterial cells have no well-defined nucleus or nuclear membrane; they have a region called the nucleoid. A light microscope used in school magnifies 100 to 400 times; an electron microscope magnifies about 10,00,000 times.

Cell Structure and Levels of Organisation: formulas and key facts

Basic parts of a cell: Cell membrane
Cytoplasm
Nucleus; Present in plant, animal, and (membrane and cytoplasm) bacterial cells.
Extra parts in a plant cell: Cell wall
Plastids (chloroplasts)
Large vacuole; Fungal and bacterial cells also have a cell wall; fungi have no chloroplasts.
Levels of organisation: Cell > Tissue > Organ > Organ system > Organism; Cell is the basic unit of life.
Bacterial cell: Nucleoid instead of a well-defined nucleus; No nuclear membrane.
Magnifications in the chapter: Hooke 200 to 300 times
School microscope 100 to 400 times
Electron microscope about 10,00,000 times; Quote as printed.

How to solve Cell Structure and Levels of Organisation questions

Use this method for 'identify', 'compare' and 'reason' questions on cells.

1Identify whether the cell is plant, animal, fungal or bacterial from the clues given.
2Name the parts present: membrane, cytoplasm, nucleus; then add cell wall, plastids, vacuole as clues allow.
3For a comparison, use two columns and give at least three points for each difference.
4For a function question, link the shape or part to the work (branched neuron, spindle muscle, rigid wall).
5For levels of organisation, write the sequence from cell to organism and give one example of each.
6Check that the answer uses the textbook's terms (nucleoid, cytoplasm, tissue).

Cell Structure and Levels of Organisation in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Counting cells in a magnified field

Suppose a student looks at an onion peel and sees a field of view in which 12 cells lie in a row across a 0.6 mm width. Imagine she assumes all the cells are equal in width.

(a) Find the width of one cell in mm and in micrometres (1 mm = 1000 micrometres). (b) How many cells would fit in a row across a 3 mm line? (c) Why can she see them closely packed with no gaps?

Try it first, then show the solutionSolution

Width of one cell = 0.6 mm ÷ 12 = 0.05 mm.
0.05 mm × 1000 = 50 micrometres.
Number across 3 mm = 3 ÷ 0.05 = 60 cells.
Each plant cell has a rigid cell wall, so the cells fit together compactly and look firm.

Answer: (a) 0.05 mm (50 micrometres); (b) 60 cells; (c) the rigid cell wall packs them closely.

Memory hook: Bricks in a wall: cells packed side by side.

Cell shape and function

Imagine you are told that cell P is long with branches, cell Q is spindle-shaped, and cell R is thin and flat. One is a nerve cell, one a muscle cell and one a cheek cell.

(a) Match P, Q, R to the three cell types. (b) For each, state how the shape helps. (c) Which tissue-level group would a group of Q cells form, and where in the body is it found as one example?

Try it first, then show the solutionSolution

P is the nerve cell, Q the muscle cell, R the cheek cell.
P: branches reach different parts of the body and pass messages quickly. Q: thin, flexible spindle shape can contract and relax. R: flat shape forms a protective lining.
A group of similar muscle cells forms muscle tissue, found for example in the food pipe, which pushes food to the stomach in a wave.

Answer: (a) P nerve, Q muscle, R cheek; (b) branches for messages, spindle for contraction, flat for lining; (c) muscle tissue, e.g. food pipe.

Memory hook: Form follows function: the shape of a cell is its job description.

Tricks to remember Cell Structure and Levels of Organisation

Short memory aids. Say each one aloud once, then use it on a question the same day.

MCN for every cell
Membrane, Cytoplasm, Nucleus: the three basic parts of an ordinary cell.
Use it when: Quick recall of the basic parts.
Wall, Plastid, Vacuole = plant extras
Think of a plant as a 'WPV': it needs a Wall for strength, Plastids for food and storage, a Vacuole for storage and shape.
Use it when: Plant versus animal cell question.
Cats Tickle Our Silly Ones
Cell, Tissue, Organ, System, Organism.
Use it when: Order of levels of organisation.
Bacteria: nucleoid, not nucleus
Nucleoid = 'nucleus-like' without a membrane.
Use it when: Bacterial cell question.

Cell Structure and Levels of Organisation: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Basic parts and functions · 3 marks · Short answerBoard level

Name the three basic parts of a cell and state one function of each.

Try it first, then show the solutionSolution

Cell membrane: encloses the cell contents and allows entry of essential materials and exit of waste. (1)
Cytoplasm: holds the other components and compounds; most life processes take place in it. (1)
Nucleus: regulates all activities and growth of the cell. (1)

Answer: Cell membrane (controls entry and exit), cytoplasm (site of life processes) and nucleus (regulates activities and growth).

Example 2: Which part is only in a plant cell · 1 mark · MCQBoard level

Which of the following is present in a plant cell but absent in a typical animal cell?
(a) Nucleus
(b) Cell membrane
(c) Cell wall
(d) Cytoplasm

Try it first, then show the solutionSolution

Nucleus, cell membrane and cytoplasm are present in both.
The cell wall is the extra outer layer in plant cells.

Answer: (c)

Example 3: Comparing plant and animal cells · 5 marks · Long answerHarder board level

Draw up a table of at least four differences between a plant cell and an animal cell using the structures named in the chapter, and give one reason why a plant cell looks firm.

Try it first, then show the solutionSolution

Cell wall: present in plant cells; absent in animal cells. (1)
Chloroplasts (plastids with chlorophyll): present in green parts of plants; absent in animal cells. (1)
Vacuole: large in plant cells; usually absent, or small, in animal cells. (1)
Shape: plant cells are usually rectangular, elongated or oval and closely packed; animal cells vary: round, spindle-shaped, branched, flat. (1)
A plant cell looks firm because the cell wall gives rigidity and strength, and the vacuole helps maintain the shape of the cell. (1)

Answer: Plant cells have a cell wall, chloroplasts and a large vacuole, which animal cells lack; plant cells are firm due to the cell wall and vacuole.

Example 4: Cell shape and function in the body · 4 marks · Case-basedHarder board level

Read the passage and answer.

A student studies a nerve cell, a muscle cell and a cheek cell. The nerve cell is very long with branches. The muscle cell is spindle-shaped. The cheek cell is thin and flat.
(a) Explain how the shape of the nerve cell helps it do its work. (1)
(b) Why is the spindle shape of a muscle cell suited to the food pipe? (1)
(c) What is the function of the cheek cells? (1)
(d) A group of muscle cells in the food pipe is an example of which level of organisation? (1)

Try it first, then show the solutionSolution

(a) The long, branched shape lets it reach different parts of the body and pass on messages quickly. (1)
(b) Muscle cells are thin and flexible, so they can contract and relax in a wave and push food down to the stomach. (1)
(c) They form a protective lining on the inner surface of the cheek. (1)
(d) A tissue, because it is a group of similar cells. (1)

Answer: (a) Reaches parts of body and carries messages fast; (b) flexible spindle cells contract in waves; (c) protective lining; (d) tissue.

Example 5: Reasoning about bacteria and eggs · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

A student says: 'Bacteria have no nucleus, so bacteria are not made of cells.' Another says: 'An ostrich egg is a huge cell, so it is not made of the same materials as a small cell.'
(a) Correct the first statement. (1)
(b) What does the bacterial cell have in place of a nucleus? (1)
(c) Which part of an ostrich egg is the single cell, and what are the other parts? (1)
(d) Correct the second statement. (1)

Try it first, then show the solutionSolution

(a) Bacteria are made of one cell (unicellular); they simply lack a well-defined nucleus and nuclear membrane. (1)
(b) A nucleoid region. (1)
(c) The yolk is the single cell; the shell protects it and the white liquid nourishes it, and these are non-cellular material. (1)
(d) The egg yolk is still a cell with the usual parts; it is just very large (about 130 mm to 170 mm in diameter), with extra non-cellular material around it. (1)

Answer: (a) Bacteria are single-celled; (b) nucleoid; (c) yolk is the cell, shell and white are non-cellular; (d) it is a cell that is simply large.

Where students lose marks in Cell Structure and Levels of Organisation

The slips examiners see most often, and what to write instead.

Mistake: Saying that a bacterial cell has a nucleus.
Students apply the plant and animal pattern to every cell.
Wrong working
Bacteria have a nucleus with a nuclear membrane.
Right working
Bacteria have no well-defined nucleus or nuclear membrane; they have a nucleoid region.
Do this: Link 'bacteria' with 'nucleoid'.
Usually costs: 1 mark.
Mistake: Saying plant cells have no cell membrane because they have a cell wall.
The wall is more visible.
Wrong working
A plant cell has a cell wall instead of a membrane.
Right working
A plant cell has a cell membrane and an extra cell wall outside it.
Do this: Wall is an addition, not a replacement.
Usually costs: 1 mark.
Mistake: Giving shapes without the function.
Questions ask 'how does the shape help' but students describe the shape only.
Wrong working
A nerve cell is long and branched.
Right working
A nerve cell is long and branched so it can reach different parts of the body and pass messages quickly.
Do this: Use 'so that' in the answer.
Usually costs: 1 mark.
Mistake: Reversing the order of tissue and organ.
Students are not sure which is bigger.
Wrong working
Cell, organ, tissue, organ system, organism.
Right working
Cell, tissue, organ, organ system, organism.
Do this: A tissue is made of similar cells; an organ is made of different tissues.
Usually costs: 1 mark.

Exam tips

For plant versus animal cell questions, give at least three points and use a table.
Always give the function when you name a cell part.
Write 'nucleoid' for bacteria; do not write 'nucleus'.
When asked about cell shape, add the reason: long and branched to carry messages quickly.
Quote magnifications as the book does: school microscope 100 to 400 times; electron microscope about 10,00,000 times.

Practice questions on Cell Structure and Levels of Organisation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
State the correct order of levels of organisation in a multicellular organism, starting from the smallest.
Hint
Cell, then the group of similar cells.
Answer
Cell, tissue, organ, organ system, organism.
Q2 · 1 mark · MCQBoard level
Who first used the word 'cell' and for what did he use it?
(a) Leeuwenhoek, for a bacterium
(b) Hooke, for the small empty compartments he saw in a thin slice of cork
(c) Hooke, for a blood cell
(d) Leeuwenhoek, for cork spaces
Hint
Think of a honeycomb.
Answer
(b)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Plant cells are compactly arranged and look firm.
Reason (R): The cell wall gives rigidity and strength to the plant cell.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Which part gives firmness?
Answer
(a) The cell wall gives rigidity and strength, so the cells fit together and look firm.
Q4 · 4 marks · Short answerHarder board level
In an onion peel slide a student sees about 40 cells in a row across a width of 2 mm. (a) Find the average width of a cell in mm. (b) Convert to micrometres. (c) Name two parts she can see in a stained onion cell that are not seen in a cheek cell. (d) Why is a stain such as safranin used?
Hint
Divide the width by the number of cells; 1 mm = 1000 micrometres. Parts: cell wall and a large vacuole.
Answer
(a) 2 ÷ 40 = 0.05 mm. (b) 50 micrometres. (c) Cell wall and a (large) vacuole. (d) The stain gives colour, so the cells are seen clearly (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
In a diagram of three cells, cell X has a nucleus, cytoplasm and membrane only; cell Y has these three plus a cell wall and chloroplasts; cell Z has membrane and cytoplasm, a cell wall and a nucleoid but no nucleus.
(a) Identify X, Y and Z. (b) Which cell can carry out photosynthesis? (c) Which cell type belongs only to unicellular organisms, and name one such organism? (d) Why can Z not be a plant cell?
Hint
Chloroplasts and the nucleoid are key clues.
Answer
(a) X animal cell, Y plant cell, Z bacterial cell. (b) Y, because it has chloroplasts. (c) Z, the bacterial cell; bacteria are unicellular, for example Lactobacillus. (d) It has a nucleoid and no well-defined nucleus, which plant cells have (1 mark each).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the basic unit of life?Show answer
The cell.
2.Name the three basic parts of a cell.Show answer
Cell membrane, cytoplasm and nucleus.
3.What does the cell wall do?Show answer
It gives rigidity and strength to the plant cell.
4.What is the largest known single cell mentioned in the chapter?Show answer
The yolk of an ostrich egg, about 130 mm to 170 mm across.
5.What do bacterial cells have instead of a nucleus?Show answer
A nucleoid region without a nuclear membrane.
6.Which scientist is called the Father of Microbiology?Show answer
Antonie van Leeuwenhoek.

Cell Structure and Levels of Organisation: frequently asked questions

Why are cheek cells and onion peel cells different in shape?

Onion peel cells have a cell wall, are nearly rectangular and packed without gaps. Cheek cells have no cell wall; they are thin, flat and polygon-shaped, and form a protective lining.

What is the difference between a tissue and an organ?

A tissue is a group of similar cells. An organ is made of different tissues that work together.

Why is a stain used for the slide?

Stains such as safranin or methylene blue increase the contrast so that cells are seen clearly. Glycerin keeps the cells from drying.

Do all cells have a vacuole?

Plant cells have a large vacuole. Animal cells usually have none, or small ones.